The invention relates generally to surveying instruments. More specifically the invention relates to a rolling, contact-based, surface profiler for determining the contour and characteristics of a surface. Such apparatus are useful in a number of industries and applications, most notably in the construction and maintenance of roads, aviation runways, bridges, buildings and other structures.
Surface profiling methods include either non-contact methods using optical (e.g. laser) and ultrasonic transducers, or contact-based methods using ground-engaging pads or wheels.
Contact-based profilers are generally either of the xe2x80x9cwalkingxe2x80x9d or the rolling type. So-called xe2x80x9cwalkingxe2x80x9d profilers include those having spaced ground-engaging pads that are alternately brought into engagement with the surface across the distance to be measured. However, the majority of contact-based profilers are of the rolling type. Rolling profilers travel on wheels over the surface to be profiled. They may be manually propelled by a walking operator, or driven or towed by a vehicle.
Rolling profilers may in turn generally be characterized as being of the type where the profiler""s supporting wheels are not connected to the transducer (typically with an inclinometer or a pendulum measuring the inclination of the entire profiler""s frame) or of the type having separate marker or sensing wheels that do not support the profiler but are connected to a transducer for direct sensing of the position of the marker wheel in relation to the supporting wheels. A relatively common prior art approach for rolling profiling apparatus of the latter type is to provide load bearing wheels at the front and rear ends of a frame and ground-engaging sensing means mounted between the load bearing wheels. Such apparatus is exemplified by U.S. Pat. No. 5,535,143 to Face.
In surface profiling, a surface contour or xe2x80x9cprofilexe2x80x9d is acquired by making measurements at constant distance intervals of the elevation along the surface, relative to a starting elevation. Sampling of elevation in this manner produces a mathematical series of elevations, which collectively represent the physical surface. The elevation series can be used for a number of purposes relating to construction or ongoing management of the surface.
Various mathematical algorithms can be applied to the series to calculate indices that are representative of the roughness or smoothness of the surface. The xe2x80x9croughnessxe2x80x9d relates to the discomfort that would be experienced by a passenger riding in a real or simulated vehicle that rolls over the surface. One of these indices, by way of example, is the International Roughness Index (IRI), that models the suspension of a nominal quarter of an automobile that is rolled over the surface within a computer model. The IRI algorithm computes the total travel of the quarter car""s suspension per unit of distance traveled while rolling over the subject profilexe2x80x94the greater the travel, the higher the IRI value or roughness.
IRI is increasingly being used for surface construction contract management. The quality of a newly constructed surface is compared to its contractual end product specification to determine if the finished or xe2x80x9cend productxe2x80x9d surface is compliant with the specification. Construction contracts can be managed using surface profilers with contract bonuses and penalties payable depending on profile test results. IRI is coming into use as the preferred index being used to determine profile quality. It should be apparent that instruments used to acquire the elevation series representing the actual surface profile that are used as input for calculation of the IRI must therefore have high accuracy and repeatability.
IRI is also being used for management of large-scale networks of roads within the jurisdictions of state departments of transport and highways, where non-contact surface profilers capable of collecting data at highway speeds are commonly being used. These are typically inertial profilers that measure elevation with reference to an inertial reference contained within a computer model. Due to their inherent limitations, such inertial profilers must be calibrated or verified against a benchmark reference or a more accurate profiling instrument to validate the data they acquire.
As the accuracy of any rolling contact-based profiler depends on maintaining continuous contact between the profiler and the surface to be profiled, the more accurate rolling profilers tend to be those that are manually operated at relatively low speeds so that the characteristics of the surface can be fully captured. While the accuracy of such devices is generally higher, the rate of data collection using contact devices has generally been too slow.
Prior art rolling devices, travelling at speeds approaching normal human walking speed of about 2.5 mile per hour, begin to lose contact with the surface to be profiled, particularly when travelling over holes or bumps. As a result, the operator must restrict the speed of the profiler to avoid bouncing it and such profilers require substantial time to collect data, requiring the operator to remain in the field for extended periods. This in turn subjects the operator to risks from the traffic in the area being surveyed. In addition, despite care being taken by the operator to avoid bounce, the accuracy of some of these devices is still less than ideal.
It is therefore an object of the present invention to provide a rolling profiler having improved accuracy and increased speed of data acquisition. More specifically, it is an object of the present invention to provide such improved accuracy and increased speed in a rolling profiler wherein the transducer measures the inclination of the entire profiler frame.
It is known to provide, in a rolling profiler, a suspension system between load bearing wheels and the frame of the profiler, which supports inclinometer transducer means, in a manner analogous to a conventional vehicle suspension. Such a system is disclosed for example in U.S. Pat. No. 3,882,607 to Plasser et al. in a rail profiling car. The effect of such a suspension is to smooth out the ride of the frame. However, where the transducer measures the inclination of the frame, this results in an averaging of the profile data and detracts from the accuracy of the profile.
It is desirable to provide a means for maintaining the supporting wheels of the profiler in continuous contact with the surface but to do so by means of a bias system that nonetheless allows the frame to fully track the vertical displacement of the wheels caused by discontinuities in the surface being profiled.
It is further known to provide a handle to allow an operator to propel a manual rolling profiler. Such handles are disclosed in U.S. Pat. No. 3,026,164 to Lancerini and U.S. Pat. No. 5,107,598 to Woznow et al. It will be noted that such prior art handles are typically either rigidly mounted at the rear end of the profilers or are pivoted high above the wheel axles. However, such arrangements subject the frame of the profiler to an unbalanced vertical force as a result of the propulsion and manipulation (pushing and pulling) by the operator of the handle. This unbalanced vertical force on the frame skews the derived profile data.
It is therefore a further object of the present invention to provide a handle arrangement that minimizes the imbalance imposed on the frame as a result of manipulation by the operator.
With the higher accuracy and higher speed of operation contemplated by the present invention, it is possible to operate the profiler at speeds greater than the normal walking speed of an operator. It is therefore desirable to provide means for converting the profiler from a manual mode to a driven mode.
The foregoing and other objects of the invention will be appreciated by reference to the summary and detailed description of the preferred embodiment that follow.
The surface profiling apparatus to which the invention relates comprises a frame, wheels and one or more devices for measuring inclination of the frame. Such devices are preferably inclinometers.
In one embodiment of the apparatus, the frame is supported by front and rear load bearing wheels mounted on the frame.
According to one aspect of the invention, at least one mass is resiliently supported by the frame (not between the frame and the wheels) to provide a downwardly biasing force on the frame. The resilient support for the masses is sometimes referred to herein and in the claims as a suspension and the masses in such arrangement are sometimes referred to as xe2x80x9cfloating massesxe2x80x9d. The invention acts to maintain the wheels in close contact with the surface to be profiled, while eliminating relative vertical displacement of the wheels in relation to the frame. Preferably the mass is larger than the combined mass of the frame and wheels and consists of a battery.
In a more specific aspect of the invention, one mass is associated with a front portion of the frame and another mass is associated with a rear portion of the frame.
The tracking of the wheels and frame supporting the inclinometer(s) is improved by the introduction of such resiliently supported masses bearing down on the front and rear frame portion, the masses being preferably suspended above the wheels and preferably constrained for movement in a direction that is substantially perpendicular to the longitudinal axis of the frame. More specifically the movement is preferably normal to the general plane of the surface being profiled, i.e. vertical in relation to the frame of the apparatus.
The masses provide a downward force and inertia that opposes vertical motion of the frame. Such vertical motion may result from the wheel(s) passing over bumps in the surface to be profiled and would tend to thrust upward the wheel and consequently the frame. Absent the mass system of the invention, this would normally result in separation of the wheel from the surface to be profiled and error in the data acquired by the inclinometer(s) mounted on the frame.
The masses are resiliently, rather than rigidly, supported, for example as by a spring. The compliance of the suspension/support allows initial relative upward movement of the frame in relation to the masses. The suspension""s resiliency then acts to apply a downward force to the frame following the initial upward displacement.
A suspension having multiple degrees of freedom may be subject to troublesome oscillation in the lateral plane that would skew the profile data. Consequently, the invention substantially constrains the direction of movement of the masses to the vertical plane (in relation to the frame).
Sustained underdamped oscillation in the vertical plane is also undesirable as it may thwart the objective of maintaining close contact between the wheels and the surface to be profiled. Accordingly, in one aspect the invention contemplates the use of dampers associated with the suspension.
The accuracy of the surface profiling process may be improved by eliminating or reducing instrument bias arising from both mechanical sources and sensor sources, i.e. reducing the tendency for the surface profile curve shape, produced from data acquired by the profiler, to deviate or drift from the true profile curve shape. Such bias would be apparent from a tendency of the inclinometer(s) to read higher or lower than the correct value for a sustained number of samples. IRI is very sensitive to bias error in profile data so such error is very undesirable.
In one of its aspects, the present invention reduces mechanical bias by providing a pivoting coupling for the propulsion means to the profiler frame at a point substantially central between the front and rear wheels, that is, at the center point of a line joining the centers of the wheel axles. Use of either a fixed (non-pivoting) coupling or selection of a point of pivoting coupling of the propulsion means at any other point on the frame would result in a torquing of the frame about the lateral axis, with respect to the direction of travel. This torque would be apparent from analysis of force vectors acting on the frame which would resolve as an unbalanced moment about the center of the profiler""s frame. The said torque would specifically result from thrust on the propulsion handle in combination with frictional forces associated with the rotation of wheels on their bearings and rolling friction between the wheels and the surface to be profiled. The said torque would result in unbalanced vertical loading on the two axles and, given the compliance of the rubber wheels, would consequently result in a tilt of the instrument chassis, which would in turn be detected by the inclinometer and result in said bias error.
In a further aspect, the present invention reduces sensor bias error by the use of two or more (any even number) of identical inclinometer sensors attached to the frame of the profiler. The odd and even numbered sensors are oriented in reverse with respect to each other along the axis of travel, such that odd numbered sensors are oriented 180 degrees with respect to the even sensors. The outputs of the odd and even numbered inclinometers are subtracted from each other with the result that the desired signal is averaged and unwanted drift signal is largely cancelled out. This is possible because inclinometers and other sensors manufactured with identical design and manufacturing processes will typically have drift characteristics that are usually fairly closely matched both in polarity and magnitude.
In another aspect of the invention, the first floating mass is provided over the front wheel or wheels and the second floating mass is provided over the rear wheel or wheels.
In yet another aspect of the invention, the movement of each floating mass is constrained to be substantially in the vertical plane by a longitudinally rigid member attached for rotation about a point on the end of the frame opposite the wheel over which the mass is located.
In a more detailed aspect of the invention, each mass is secured by means of at least one tie rod extending from the mass to the opposite end of the frame and secured to a pivoting suspension bar.
In yet a further aspect of the invention, the floating masses are supported by means of springs between each floating mass and a portion of the frame underlying the respective masses. Advantageously, dampers are associated with the suspension supports for the masses.
In yet another aspect, the invention provides a pivoting handle and hitch arrangement allowing the handle to be hitched to a motorized drive unit for remotely propelling the profiler.
The present invention, given its high accuracy and repeatability, while finding uses in several industries and for many purposes, will be of particular value in both the contract management of new surface construction and as a reference standard for certification of other instruments.
The foregoing was intended as a broad summary only and of only some of the aspects of the invention. It was not intended to define the limits or requirements of the invention. Other aspects of the invention will be appreciated by reference to the detailed description of the preferred embodiment and to the claims.